Described is an arrangement for retaining a bearing, designed in particular to support a high-pressure compressor shaft, without this application be restrictive.
The construction of turbomachines demands complicated layouts because of the nesting of the high-pressure compressor and turbine stage inside the low-pressure turbine and compressor stage and because of the presence of two concentric runs of shafts each of which connects the compressor of one stage to the corresponding turbine. This complication is encountered above all during machine maintenance, when the machine has to be disassembled then reassembled.
A particular problem arises in the case of the high-pressure compressor. If we examine FIG. 1, which depicts an aircraft engine in longitudinal section, a rotor 1 is engaged in the center of a stator 2 and conventionally comprises a fan 3, a low-pressure compressor 4, a high-pressure compressor 5, a high-pressure turbine 6 and a low-pressure turbine 7 which are aligned from front to rear. All of these elements carry blades which alternate with stationary vanes of the stator 2 and, like those, are located in an annular stream 8 through which the gases flow; a combustion chamber 9 is arranged in the annular stream 8 between the high-pressure turbine 6 and compressor 5, and allows the fuel injected further upstream in the stream 8 to be burnt and thus produce combustion gases which drive the turbines 6 and 7. There is also a run of high-pressure shafts 10 connecting the high-pressure compressor 5 to the high-pressure turbine 6 and a run of low-pressure shafts 11 extending into a cavity 12 of the previous run of shafts 10 and which connects the low-pressure compressor 4 to the low-pressure turbine 7.
The high-pressure run of shafts 10 comprises, in particular, a high-pressure compressor stub shaft 13 around which is engaged a bearing 14 which supports it via a rib 15 belonging to the stator 2. Referring to FIG. 2 now for a more detailed examination, it can be seen that the bearing 14 is a rolling bearing, the inner ring 16 of which is slipped around the stub shaft 13 and held in place by a stop ring 17, it too being slipped around the stub shaft 13 from its end face 18 and which presses the inner ring 16 backwards, against an opposed stop ring 19 which touches a step 20 of the stub shaft 13. The inner ring 16 is kept clamped between the stop rings 17 and 19 by a nut 21 which, on its interior face, has a screw thread 22 engaged in a screw thread 23 made on the stub shaft 13 near the end face 18: by tightening the nut 21, the stop ring 17, the inner ring 16 and the opposite stop ring 19 are pushed back in turn before this stack of components is compressed against the step 20. The arrangement is supplemented by a locking piece 24, the purpose of which is to prevent the nut 21 from working loose as a result of vibration; this locking piece 24 is engaged in the cavity 12 and held in place in the stub shaft 13 by a circle of splines 25 engaged in corresponding splines belonging to the stub shaft 13 and by curved-over ends 26 of flexible tabs 27 engaged in a groove 28 in the stub shaft 13. The first of these connecting means prevents the locking piece 24 from rotating and the second prevents its translational movement, with respect to the stub shaft 13. The flexible tabs 27 are further supplemented by engagement tongues 29, adjacent to the curved-over ends 26. However, the locking piece 24 also comprises a circle of teeth 30, protruding from the cavity 12 and which engage between complementary teeth 31, also arranged in a circle and produced on a portion 32 of the nut 21 which extends inwards, in front of the end face 18 of the stub shaft 13, which it covers. For the sake of preciseness, it is added that the teeth 30 are at the front of the locking piece 24, the flexible tabs 27 at the rear, and the curved-over ends 26 and the engagement tongues 29 at the rear of the tabs 27.
To remove the high-pressure compressor 5 to which the stub shaft 13 belongs, this shaft needs to be disengaged from the bearing 14. A preliminary step consists of removing the low-pressure turbine 7 so that a high-pressure turbine shaft 33 which belongs to the line of low-pressure shafts 11 and occupies most of the cavity 12 can be extracted, by pulling it backwards. An appropriate tool with claws is then inserted around the engagement tongues 29 to press against them and push them all towards the axis of the machine by curving the flexible tabs 27, whereby the curved-over ends 26 come out of the groove 28 and the locking piece 24 can then be pulled backwards to extract its splines 25 from the splines of the stub shaft 13 and to disengage its teeth 30 from the teeth 31.
It would then seem possible to unscrew the nut 21 using a tool engaged between the teeth 31, but such an operation is actually premature because a low-pressure compressor shaft 34, also belonging to the run of low-pressure shafts 11, has remained in place and extends just in front of the nut 21: the axial space denoted I which separates them is smaller than the length, denoted J, by which the nut 21 is engaged on the stub shaft 13. It is therefore necessary also to remove the low-pressure compressor 4 and its shaft 34 before the high-pressure compressor 5 can be removed, this being an operation which is not necessarily useful. What is more, removing the low-pressure compressor 4 itself may be complicated and need to be preceded by the removal of other parts of the machine, for example a gearbox which has not been depicted in the figures. All of this means that removing the high-pressure compressor 5 is a lengthy and tiresome operation that cannot be made any easier by enlarging the space I, as this would entail reviewing the entire design of the machine and would increase its size.
The object of the invention therefore consists in facilitating the removal of such an arrangement for retaining a bearing comprising a stop, a clamping nut and a locking piece by reducing the preliminary manual interventions intended to free these parts, so that the bearing can be separated from the stub shaft it supports. The advantages of the invention are obvious with an arrangement of runs of shafts such as the one just described because there is no longer the need to remove parts in front of the front end of the stub shaft, and access to just one side of the retaining arrangement, from which the stub shaft will be removed, will suffice. To do this, a novel type of retaining arrangement is proposed. In its most general design, the arrangement, arranged around a stub shaft in which is machined a cavity and which is bounded by an end face, comprises a ring forming a stop for the bearing, a nut for clamping the ring and a piece for locking the nut, the locking piece being held in the cavity of the stub shaft by removable means of attachment and connected to the nut by imbricated teeth arranged in a circle on the nut and on the locking piece, and it is characterized in that the ring comprises an interior portion covering the end face of the stub shaft as far as the cavity and equipped with a screw thread for screwing onto a thread of the nut, and the nut is placed in the cavity and comprises a stop face directed towards the end face and engaged against a stop face standing up from the stub shaft in the cavity.
Further light will be shed on the nature of this new arrangement and on its advantages using the following figures, in addition to FIGS. 1 and 2 already described and which depict a turbomachine and that portion thereof which bears a conventional retaining arrangement.